Manufacturing process for surge arrestor module using compaction bladder system

ABSTRACT

The present disclosure is directed to a method of producing a surge arrestor module, comprising the acts of (i) providing a plurality of MOV blocks arranged in a stack, (ii) applying an epoxy-reinforced structural layer to an outer surface of the stack, (iii) after the applying, inserting the stack into a flexible bladder, and (iv) curing the epoxy-reinforced structural layer with elevated temperatures while the flexible bladder applies radially aligned pressure to the stack and a tool applies axially aligned pressure to the stack. The present disclosure also includes an apparatus for performing the methods described herein. The apparatus includes an outer case structure and a flexible bladder that fits within the outer case structure. A hollow inner region of the outer case structure is pressurized to force the flexible bladder against the surge arrestor module as the surge arrestor module is curing.

COPYRIGHT

A portion of the disclosure of this patent document may contain materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patentdisclosure, as it appears in the Patent and Trademark Office patentfiles or records, but otherwise reserves all copyright rights whatsoever

FIELD OF THE INVENTION

The present invention relates to surge arrestor modules that protectequipment from electrical disturbances. More particularly, thisinvention relates to a process for making a surge arrestor having aseries of metal oxide varistor (MOV) blocks in contact with each otherand a fiberglass-reinforced layer that surrounds the MOV blocks.

BACKGROUND OF THE INVENTION

A surge arrester is a protective device that is commonly connected inparallel with a more expensive piece of electrical equipment to divertcurrent surges from over-voltage conditions safely around the electricalequipment. When exposed to the over-voltage condition, the surgearrester operates in a low impedance mode that provides a current pathto electrical ground. By doing so, the surge arrestor protects theinternal circuitry of the electrical equipment from damage due to theover-voltage condition. After an over-voltage condition has beenexperienced, the surge arrester returns to operation in the highimpedance mode in which the surge arrester provides a current path toground having a relatively high impedance.

Surge arrestors are often made from a stack of MOV blocks. Each MOVblock is characterized by having a relatively high resistance whenexposed to a normal operating voltage, and a much lower resistance whenexposed to a higher voltage, such as a higher voltage associated withover-voltage conditions. The number of MOV blocks in a stack and/or thelength of each MOV block is selected to support various system voltages.There are two contacts at the end of each MOV stack. The contact on oneend is typically configured with a lug-style interface for attaching toa bushing and the contact on the other end is typically a copper tubewith a crimp barrel (or other connecting structure) for attaching aground wire.

Each MOV block in the stack must maintain proper electrical contact withthe adjacent MOV blocks so as to reduce the contact resistance.Furthermore, the magnitude of the current in over-voltage conditions canbe significant and produce high electromechanical forces on the surgearrester stack. For these reasons, surge arrester stacks must be madefrom high strength materials and are placed under compression loads. Toprovide the compression loading, the individual MOV blocks are typicallyheld together by a fiberglass reinforcing structure applied to theoutside surfaces for increased physical strength. For use in shieldeddistribution devices, the surge arrester's fiberglass reinforcingstructure must be free of voids or air pockets. Any air voids within thefiberglass or between the fiberglass and outside surface of the MOVblocks could cause electrical discharge once energized and wouldultimately result in a failure of the device.

One known method for applying the fiberglass onto the surge arresterstack is to use fiberglass sheet that is pre-impregnated with epoxyresin and wrapped several times around the MOV blocks and end contactsto build up the desired wall thickness. The epoxy resin, when heated,cures and solidifies to form a very high strength substrateencapsulating the MOV blocks and end contacts. While curing in the oven,the fiberglass and pre-impregnated epoxy resin must be compressed toeliminate air voids between the wrapped layers of the pre-impregnatedfiberglass. One method for compressing the pre-impregnated fiberglassknown in the industry is disclosed in U.S. Pat. No. 8,117,739, whichuses a shrink film radially wrapped over the outside of the fiberglassthat shrinks when exposed to heat. This shrinking of the film exerts acompaction force on the fiberglass and epoxy while it is being heatedand cured.

There are at least two main issues with the use of shrink film tocompact the fiberglass and epoxy while curing. One issue is that thelevel of compaction cannot be varied. The level of compaction isdictated by the shrink ratio of the film material being used and cannotbe varied or increased, if needed. As the layers of fiberglass wrappingincrease to achieve increased strength, the amount of compaction forceneeded to eliminate any air voids also increases. Another issue thatarises when using shrink film for compaction is that after the film isremoved, there are impressions left on the fiberglass/epoxy in the areaswhere the shrink film overlapped itself. This results in the fiberglassand epoxy needing to be sanded and smoothed out after curing in the ovenand removing the shrink film. This additional operation of cleaning thefiberglass surface is not desirable and requires a lot of attention bythe operator to ensure a smooth surface that is free of any dents orscratches.

Consequently, there is a need for a more reliable and efficient methodof making surge arrestors. The present disclosure provides a new methodfor producing a surge arrestor stack that helps to eliminate air gaps,provides consistency in the outer surfaces of the stack, and that candeliver a variable amount of force during the curing process. All theseand other objects of the present invention will be understood throughthe detailed description of the invention below.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a method ofproducing a surge arrestor module, comprising the acts of (i) providinga plurality of MOV blocks arranged in a stack, (ii) applying anepoxy-fiberglass layer to an outer surface of the stack, (iii) placingthe stack with the applied epoxy-fiberglass layer into a flexiblebladder, and (iv) while the epoxy-fiberglass layer is curing around theouter surface of the stack, applying pressure to the flexible bladder togenerate a compressive force to the epoxy-fiberglass layer and thestack.

In another aspect, the present invention is directed to a method ofproducing a surge arrestor module, comprising the acts of (i) providinga plurality of MOV blocks arranged in a stack, (ii) applying anepoxy-reinforced structural layer to an outer surface of the stack,(iii) after the applying, inserting the stack into a flexible bladder,and (iv) curing the epoxy-reinforced structural layer with elevatedtemperatures while the flexible bladder applies radially alignedpressure to the stack and a tool applies axially aligned pressure to thestack.

In a further aspect, the present invention is an apparatus for producinga surge arrestor module, comprising an outer case structure, a flexiblebladder, and a pressure source. The outer case structure has an innersurface and an outer surface. The inner surface forms a hollow region.The outer case structure including a port that provides access to thehollow region. The flexible bladder is located within the hollow region.The flexible bladder is sized and configured to receive thesurge-arrestor stack. The surge arrestor stack has a plurality of MOVblocks and a layer of epoxy-reinforced structural material on exteriorsurfaces of the plurality of MOV blocks. The pressure source deliverspressurized air into the hollow region of the outer case structure viathe port. The pressurized air forces the flexible bladder to compressagainst the surge-arrestor stack while the epoxy-reinforced structuralmaterial cures.

Additional aspects of the invention will be apparent to those ofordinary skill in the art in view of the detailed description of variousembodiments, which is made with reference to the drawings, a briefdescription of which is provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with greater specificity andclarity with reference to the following drawings, in which:

FIG. 1 illustrates a typical surge arrestor assembly that utilizes asurge arrestor module.

FIG. 2 illustrates a side view of a surge arrestor module within theassembly of FIG. 1 .

FIG. 3 illustrates a cross-sectional view of the surge arrestor moduleof FIG. 2 taken along line 3-3 in FIG. 2 .

FIG. 4 illustrates a side view of a pressure fixture for manufacturingthe surge arrestor module of FIGS. 2-3 .

FIG. 5 illustrates a cross-sectional view of the pressure fixture ofFIG. 4 .

FIG. 6 illustrates a mounting frame for manufacturing multiple surgearrestor modules.

While the invention is susceptible to various modifications andalternative forms, specific embodiments will be shown by way of examplein the drawings and will be described in detail herein. It should beunderstood, however, that the invention is not intended to be limited tothe particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawings will herein be described in detail with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit the broadaspect of the invention to the embodiments illustrated. For purposes ofthe present detailed description, the singular includes the plural andvice versa (unless specifically disclaimed); the words “and” and “or”shall be both conjunctive and disjunctive; the word “all” means “any andall”; the word “any” means “any and all”; and the word “including” means“including without limitation.”

FIG. 1 illustrates one exemplary surge arrestor assembly 10 thatincludes a housing 12. The surge arrestor assembly 10 is electricallycoupled to a ground wire 14 through a lower sealing cap 16. The upperportion of housing 12 includes an interface device 18 that allows forelectrical coupling to an incoming wire or connector associated with theelectrical equipment (not shown) that requires surge protection. Thehousing 12 of the surge arrestor assembly 10 encases a surge arrestormodule 20 that provides the path for electrical current to reach theground wire 14 when over-voltage conditions are experienced by theelectrical equipment. The surge arrestor module 20 includes aground-wire connector 22 to be coupled to the ground wire 14 and aninterface connector 24 for connection to the interface device 18. Itshould be understood that the surge arrestor module 20 can be used withother styles and configurations for surge arrestor assemblies. Thedetails of the surge arrestor module 20 and its method of manufacturingare discussed in more detail below.

FIGS. 2 and 3 illustrate, respectively, a side view and across-sectional view of the surge arrestor module 20. Between theground-wire connector 22 and the interface connector 24, the surgearrestor module 20 includes a plurality of metal oxide varistor (MOV)blocks 28 that are arranged in a stack. The number of MOV blocks 28,their diameters, and their lengths (as measured along the long axis ofthe surge arrestor module 20) can vary depending on the electricalprotection specifications of the surge arrestor module 20. As shown inFIG. 3 , the axial length “X” of the surge arrestor module 20 istypically between 7 inches and 20 inches, and the diameter “Y” istypically between 1 inch and 3 inches. In one exemplary embedment, theaxial length “X” of the surge arrestor module 20 is about 12 inches andthe diameter “Y” is about 1.5 inches. In some embodiments in which alesser number of MOV blocks 28 is needed for a lower voltage stack, aMOV block 28 may be replaced with an aluminum block of the same diameterand height to permit use of the same manufacturing fixtures.

The MOV blocks 28 are held together through an epoxy-fiberglass outerlayer 26. The epoxy-fiberglass outer layer 26 is typically made from afiberglass that is pre-impregnated with an epoxy resin, which requires acuring process as described in more detail below. In the final productafter the curing process, the epoxy-fiberglass outer layer 26 generallyhas a thickness in the range of about ⅛ inch to about 3/16 inch. In onepreferred embodiment, the epoxy-fiberglass outer layer 28 has athickness of about ⅛ inch. Though the outer layer 26 is described asbeing used with a fiberglass-based material, the outer layer 26 can beused with other types of structurally reinforced materials, such ascarbon-fiber-epoxy composite materials.

The ground-wire connector 22 is in direct electrical connection with alower block contact 32, which contacts the lowermost MOV block 28. Theinterface connector 24 is in direct electrical connection with an upperblock contact 34, which contacts the uppermost MOV block 28. Asillustrated, the ground-wire connector 22 and the lower block contact 32are two separate pieces that are connected. But in other embodiments,these two pieces 22 and 32 can be a unitary piece. Similarly, theinterface connector 24 and the upper block contact 34 are illustrated astwo separate pieces that are connected. But in other embodiments, theycan be a unitary piece. In one embodiment, the upper and lower contacts32, 34 have circumferentially arranged grooves machined into theirsurfaces to help retain them on the MOV blocks 28. After wrapping a fewlayers of the epoxy-reinforced fiberglass sheet over the MOV blocks 28and the contacts 32, 34, stainless steel wire is wrapped around thecontacts 32, 34 and tensioned to pull the fiberglass layers into thegrooves of the contacts 32, 34. After tensioning, the stainless steelwires are tied off and the remaining layers of the fiberglass arewrapped onto the assembly, including over the stainless steel wires.When the epoxy cures (as described in more detail below), it solidifiesthe fiberglass that is wrapped into the grooves of the contacts 32, 34to lock the contacts 32, 34 and the blocks 28 together.

FIGS. 4 and 5 illustrate, respectively, a side view and across-sectional view of a pressure fixture 40 used for manufacturing thesurge arrestor module 20 of FIGS. 2-3 . The pressure fixture 40 includesan outer tubular structure 42, which may be made of steel or other rigidmaterials. The tubular structure 42 includes a port 44 for allowing afluid to enter the internal hollow region of the tubular structure 42.The tubular structure 42 includes a lower end collar 46 and an upper endcollar 47 that help to seal the ends of the tubular structure 42. In onepreferred embodiment, the lower end collar 46 and the upper end collar47 have internal female threaded surfaces for threadably engaging a malethreaded outer surface of the tubular structure 42. A moveable tool 48fits within the upper end collar 47 and engages the end region (e.g.,the upper block contact 34) of the surge arrestor module 20 adjacent tothe interface connector 24. The moveable tool 48 can be moved upwardlyand downwardly via rotation of a threaded screw 49.

As shown best in FIG. 5 , the surge arrestor module 20 is located withina flexible bladder 50, which itself fits within the outer tubularstructure 42. The flexible bladder 50 is preferably generallycylindrical in shape and has an inner dimension that is about the sameas the outer diameter of the surge arrestor module 20. The flexiblebladder 50 is typically made of natural rubber or synthetic rubber andhas a wall thickness of about ¼ inch to about 5/16 inch.

The inner wall surface of the flexible bladder 50 is designed to placepressure against the epoxy-fiberglass layer 26 that surrounds the stackof MOV blocks 28. A pair of bladder sealing rings 52 and 54 are located,respectively, at the lower and upper regions of the flexible bladder 50to seal the flexible bladder 50 against the lower end collar 46 and theupper end collar 47. As such, when air is pumped into the port 44 of thetubular structure 42 of the fixture 40, the outer surface of theflexible bladder 50 is acted upon by the air pressure, causing theflexible bladder 50 to provide a compressive force against theepoxy-fiberglass layer 26. A small gap between the outer surface of theflexible bladder 50 and the inner surface of the tubular structure 42allows the air to flow entirely around the flexible bladder 50, therebycreating an equal amount of pressure on the surface, which istransferred into the epoxy-fiberglass layer 26. The applied pressure ofthe flexible bladder 50 is beneficial during the curing process of theepoxy-fiberglass layer 26, as described below. Though the illustratedembodiment is described as using air pressure on the flexible bladder50, the present invention contemplates other fluids (e.g., other gasesor liquids) may be used within the tubular structure 42 to supply thepressure to the flexible bladder 50.

In manufacturing the surge arrestor module 20, the epoxy-fiberglasslayer 26 requires a curing process in which it hardens on the MOV blocks28 to strengthen the overall surge arrestor module 20. Initially, theepoxy-fiberglass layer 26 is created by fiberglass material that ispre-impregnated with an epoxy resin that is wrapped (usually multipletimes) around the stack of the MOV blocks 28. The stack of the MOVblocks 28 has the ground-wire connector 22 and the lower block contact32 located against the lowermost MOV block 28. The interface connector24 and the upper block contact 34 are located against the uppermost MOVblock 28.

In one embodiment, to keep the flowable epoxy resin contained during thecuring process, a thin layer of polyvinylidene chloride (PVDC) orpolyethylene (e.g., about 0.0005 inches to 0.0015 inch in thickness) isused as an outer layer for the stack to inhibit the epoxy from directlycontacting the flexible bladder 50. During the curing process, the thinouter layer of polyvinylidene chloride or polyethylene is absorbed intoand becomes a part of the stack. Once this wrapping process iscompleted, the stack of MOV blocks 28 with the uncured epoxy-fiberglasslayer 26 (and preferably the thin PVDC or polyethylene layer) is theninserted into the flexible bladder 50. The flexible bladder 50 is theninserted into the tubular structure 42. In one embodiment, the insidediameter of the end collars 46 and 47 are configured to allow theuncured wrapped stack to pass through them for placement in the tubularstructure 42.

As shown in FIG. 5 , the moveable tool 48 fits within the upper end cap47. The threaded screw 49 is threadably connected to a top wall 60 ofthe pressure fixture 40 via a female threaded nut 62 that is fixed intothe top wall 60. When the threaded screw 49 is rotated, it moves themoveable tool 48 upwardly and downwardly relative to the upper end cap47. As the moveable tool 48 moves downwardly, the lowermost end of themoveable tool 48 engages the upper block contact 34 so as to apply acompressive force during curing. A bottom wall 64 of the pressurefixture 40 includes a protruding structure 66 that is hollow so as toreceive the ground-wire connector 22 of the surge arrestor module 20. Insome embodiments, the protruding structure 66 is part of the overallpressure fixture 40, but is a separate piece that is installed over theground-wire connector 22 before loading the stack into the pressurefixture 40. The bottom wall 64 includes a slot that receives theprotruding structure 66 as it is moved from the side toward the middleregion of the bottom wall 64. The protruding structure 66 has a shoulderthat presses against the bottom wall 64 and an upper surface thatengages the lower block contact 32. The protruding structure 66 is thelower base structure for supporting the stack that is compressedtogether via the threaded screw 49 and the moveable tool 48. Thus, whenthe uncured surge arrestor module 20 is placed in the fixture 40, thefixture 40 includes components (e.g., the protruding structure 66 andthe movable tool 48) that clamp the MOV block 28 and the lower and upperblock contacts 32, 34 under pressure in the axial direction. By rotatingthe screw 49, the moveable tool 48 is urged downwardly to provide axialforce to the MOV block 28 and the lower and upper block contacts 32, 34to ensure the blocks 28 and lower and upper block contacts 32, 34 are ingood contract with each other. This axial pressure on each stack ispreferably the same, which is accomplished by applying the same torque(e.g., 10 ft-lbs) to each of the screws 49 (see FIG. 6 ) of the fixtures40. Though the screw 49 can be manually rotated, it can also beautomatically rotated by a motor, such that the combination of the motorand the screw 49 acts like a screw-driven linear actuator. The fixture40 may include sensor(s) in, for example, the protruding structure 66,the movable tool 48, and the flexible bladder 50, such that the axialand radial compression forces (and pressure) are known before and duringthe curing process.

Once the pressure fixture 40 is assembled and holds the uncured surgearrestor module 20, the air pressure can be supplied to the port 44 toprovide radial compression on the uncured surge arrestor module 20 viathe flexible bladder 50. Because elevated temperatures are typicallyneeded to cure the epoxy-fiberglass layer 26, in one embodiment, theentire pressure fixture 40 is located within an oven that maintains aconstant temperature for the pressure fixture 40 and the to-be-curedsurge arrestor module 20. The air circulated into the port 44 can beunheated or heated air from the oven. The air pressure acting on theflexible bladder is typically greater than 30 PSI, greater than 40 PSI,and often great than 50 PSI. The curing temperature for theepoxy-fiberglass layer 26 (e.g., supplied by the oven) is typicallygreater than about 200° F., greater than about 220° F., greater thanabout 240° F., greater than about 280° F., or greater than about 300° F.The curing time for the epoxy-fiberglass layer 26 is typically greaterthan 1 hour, greater than 2 hours, greater than 3 hours, or greater than4 hours. In one embodiment, the air pressure is about 45 PSI, the curingtemperature is about 270° F., and the curing time is about 4 hours.

During the curing process, while the epoxy resin is softening from theelevated temperatures, the radial pressure exerted by the flexiblebladder 50 forces the air pockets within the fiberglass layer 26 to exitfrom the fiberglass layer, often at the ends of the stack. Duringcuring, the level of radial pressure can be varied by increasing ordecreasing the air pressure acting on the flexible bladder 50, whichassists in the removal of air pockets. In one preferred embodiment, thecuring temperature (e.g., from the oven) is raised slowly over time toallow more time for air bubbles to escape from the fiberglass before theepoxy becomes fully cured. After the curing cycle is complete, thepressure fixture 40 is de-pressurized and the cured surge arrestermodule 20 can be removed from the pressure fixture 40. At this point,the outside surface of the surge arrester module 20 is substantiallyfree of surface defects and is substantially smooth. The outer surfaceof the surge arrester module 20 typically does not need to be cleaned orpolished prior to installing in the housing 12 of the surge arrestorassembly 10 shown in FIG. 1 . Further, due to the increased radialcompaction pressures, the number of internal voids in thefiberglass/epoxy layer 26 of the surge arrestor module 20 issubstantially reduced or eliminated. The thickness of thefiberglass/epoxy layer 26 is reduced by about 0.05 inch to about 0.1inch due to the radial compressive forces during the curing process.

FIG. 6 illustrates a mounting frame 70 for simultaneously manufacturingmultiple surge arrestor modules by use of multiple pressure fixtures 40a-40 e. The mounting frame 70 includes a base 72 allowing the mountingframe 70 to stand upright and receive multiple pressure fixtures 40 a-40e. Although five stations are shown to receive the five pressurefixtures 40 a-40 e, the mounting frame 70 can include any number ofstations for receiving the mounting fixture(s) 40.

Each of the pressure fixtures 40 a-40 e is mounted between the bottomwall 64 of the mounting frame 70 and the top wall 60. The top wall 60includes the threaded nuts 62 for receiving the screws 49 for each ofthe pressure fixtures 40. In FIG. 6 , the heads of the screws 49 are notshown as they are behind the framework adjacent to the top wall 60. Themounting frame 70 is open in the middle region to provide access for airlines that mate with the ports 44 a-44 e of the five pressure fixtures40 a-40 e. The mounting frame 70 and the related components (e.g., airlines) are designed to fit within a commercial oven for curing the fivesurge arrestor modules 20 that are located within the five pressurefixtures 40 a-40 e.

These embodiments and obvious variations thereof is contemplated asfalling within the spirit and scope of the claimed invention, which isset forth in the following claims. Moreover, the present conceptsexpressly include any and all combinations and subcombinations of thepreceding elements and aspects.

We claim:
 1. A method of producing a surge arrestor module, comprising:providing a plurality of MOV blocks arranged in a stack; applying anepoxy-fiberglass layer to surround an outer surface of the stack;placing the stack with the applied epoxy-fiberglass layer into aflexible bladder, the flexible bladder being located in an outer tubestructure; and while the epoxy-fiberglass layer is curing around theouter surface of the stack, applying air pressure between an outersurface of the flexible bladder and an inner surface of the outer tubestructure to generate a compressive force to the epoxy-fiberglass layerand the stack.
 2. The method of claim 1, further including, applyingheat to create a curing temperature that is greater than 200° F.
 3. Themethod of claim 2, further including, after the curing, releasing thepressure to the flexible bladder, and removing the stack with the curedepoxy-fiberglass layer from the flexible bladder.
 4. The method of claim1, wherein the epoxy-fiberglass layer is comprised of anepoxy-impregnated fiberglass material that is wrapped around the stackmultiple times before the act of placing the stack into the flexiblebladder.
 5. The method of claim 1, wherein the air pressure increasesthe size of a gap between the outer surface of the flexible bladder andthe inner surface of the outer tube structure during the curing process.6. The method of claim 5, wherein the air pressure is at least 30 psi.7. The method of claim 1, further including, while the epoxy-reinforcedfiberglass layer is curing around the outer surface of the stack,applying axial pressure to the stack to force the plurality of MOVblocks into tight engagement.
 8. The method of claim 7, wherein theaxial pressure is applied by at least one screw that is coupled to amoveable press tool adjacent to an end region of the outer tubestructure.
 9. The method of claim 1, wherein the epoxy-fiberglass layeris in direct contact with the outer surface of the stack whensurrounding the outer surface of the stack.
 10. A method of producing asurge arrestor module, comprising: providing a plurality of MOV blocksarranged in a stack; surrounding the stack with an uncuredepoxy-reinforced structural layer; after the applying, inserting thestack into a flexible bladder that is located in an outer tubestructure; and curing the epoxy-reinforced structural layer withelevated temperatures while the flexible bladder applies radiallyaligned pressure to the stack and a tool applies axially alignedpressure to the stack, the radially aligned pressure being due to airpressure between an outer surface of the flexible bladder and an innersurface of the outer tube structure.
 11. The method of claim 10, whereinthe air pressure increases the size of a gap between the outer surfaceof the flexible bladder and the inner surface of the outer tubestructure during the act of curing.
 12. The method of claim 10, whereinthe axially aligned pressure is due to rotation of least one screw thatis coupled to the tool, the rotation of the at least one screw axiallymoving the tool toward the stack.
 13. The method of claim 10, whereinthe epoxy-reinforced structural layer is an epoxy-impregnated fiberglassmaterial that is wrapped around the stack multiple times before the actof inserting the stack into the flexible bladder.
 14. The method ofclaim 10, further including applying an outer layer of material to theepoxy-reinforced structural layer to serve as a barrier between theflexible bladder and the epoxy-reinforced structural layer, the outerlayer of material being a thin layer of PVDC material or apolyethylene-based material.
 15. An apparatus for producing a surgearrestor module, comprising: an outer case structure having an innersurface and an outer surface, the inner surface forming a hollow region,the outer case structure including a port that provides access to thehollow region; a flexible bladder located within the hollow region, theflexible bladder being sized and configured to receive thesurge-arrestor stack, the surge arrestor stack having a plurality of MOVblocks and a layer of epoxy-reinforced structural material on exteriorsurfaces of the plurality of MOV blocks; and a pressure source fordelivering pressurized air into the hollow region of the outer casestructure via the port, the pressurized air forcing the flexible bladderto compress against the surge-arrestor stack while the epoxy-reinforcedstructural material cures.
 16. The apparatus of claim 15, wherein thepressurized air is heated air to assist with the curing process.
 17. Theapparatus of claim 15, further including at least one moveable presstool that applies compressive force along a central axis of thesurge-arrestor stack during the curing process.
 18. The apparatus ofclaim 17, wherein the moveable press tool is driven by a screw thaturges the moveable press tool toward the surge-arrestor stack.
 19. Theapparatus of claim 17, wherein the flexible bladder provides acompressive force to the surge-arrestor stack in a radial directionrelative to the central axis.
 20. A method of producing a surge arrestormodule, comprising: providing a plurality of MOV blocks arranged in astack; applying an epoxy-fiberglass layer to surround an outer surfaceof the stack; placing the stack with the applied epoxy-fiberglass layerinto a flexible bladder; applying heat to create a curing temperaturethat is greater than 200° F.; while the epoxy-fiberglass layer is curingaround the outer surface of the stack, applying pressure to the flexiblebladder to generate a compressive force to the epoxy-fiberglass layerand the stack; and after the curing, releasing the pressure to theflexible bladder, and removing the stack with the cured epoxy-fiberglassfrom the flexible bladder.
 21. The method of claim 20, wherein theepoxy-fiberglass layer is in direct contact with the outer surface ofthe stack when surrounding the outer surface of the stack.
 22. Themethod of claim 20, further including, while the epoxy-reinforcedfiberglass layer is curing around the outer surface of the stack,applying axial pressure to the stack to force the plurality of MOVblocks into tight engagement.